Pakistani security officials and rescue workers examine the site of car bombing on the outskirts of Peshawar, Pakistan, Sunday, June 2013. A car bomb exploded as a convoy of paramilitary troops passed through the outskirts of the northwest Pakistani city of Peshawar, killing more than a dozen people and wounding scores of others, police said. Mohammad Sajjad/AP

Twin bombings June 30, killed 28 people, primarily Shiites, in Pakistan's city of Quetta. More than 300 Shiite muslims have been killed in a string of major attacks in Pakistan since the start of 2013. Despite country-wide protests among Shiites and supporters since the start of the year, the state has yet to carry out a crackdown against militant groups.

1.
Who is responsible?

Sipah-e-Sahaba Pakistan (SSP) and Lashkar-e-Jhangvi (LeJ), both Sunni militant groups, have taken responsibility for the bulk of attacks against Shiite Muslims in Pakistan. Both of the groups are adherents of the Deobandi school of Islam, known for its hardline stance against many common and popular religious practices carried out on the Indian subcontinent.

SSP was established in the early 1980s under the reign and patronage of the second military dictator in Pakistan, Zia ul-Haq. LeJ broke off from SSP in 1996 after its founder, Riaz Basra, had differences with his seniors.